A Novel Role for c-Myc in G Protein–Coupled Receptor Kinase 4 (GRK4) Transcriptional Regulation in Human Kidney Proximal Tubule Cells

Abstract

The G coupled-protein receptor kinase 4 (GRK4) negatively regulates the dopaminergic system by desensitizing the dopamine-1-receptor (D1R). The expressional control of GRK4 has not been reported, but here, we show that the transcription factor c-Myc binds to the promoter of GRK4 and positively regulates GRK4 protein expression in human renal proximal tubule cells (RPTCs). Addition of phorbol esters (PMA) to RPTCs not only increased c-Myc binding to the GRK4 promoter, but also increased both phospho-c-Myc and GRK4 expression. The PMA-mediated increase in GRK4 expression was completely blocked by the c-Myc inhibitor, 10074-G5, indicating that GRK4 is downstream of phospho-c-Myc. The autocrine production of angiotensin II (Ang II) in RPTCs increased the phosphorylation and activation of c-Myc and subsequently GRK4 expression. 3-Amino-4-thio-butyl sulfonate (EC-33), an inhibitor of aminopeptidase A (APA), increased RPTC secretion of Ang II. EC-33 or Ang II increased the expression of both phospho-c-Myc and GRK4, which was blocked by 10074-G5. Blockade of the angiotensin II type 1 receptor (AT1R) with losartan decreased phospho-c-Myc and GRK4 expression. Both inhibition of c-Myc activity and blockade of AT1R restored the coupling of D1R to adenylyl cyclase (AC) stimulation in uncoupled RPTCs (uRPTCs) while PMA or Ang II caused the uncoupling of normally coupled RPTCs (nRPTCs). We suggest that the AT1R impairs D1R function via c-Myc activation of GRK4. This novel pathway may be involved in the increase in blood pressure in hypertension that is mediated by increased activity of the renin-angiotensin system and decreased activity of the renal dopaminergic system.

Long‐Term Exposure of Fine Particulate Matter Causes Hypertension by Impaired Renal D 1 Receptor–Mediated Sodium Excretion via Upregulation of G‐Protein–Coupled Receptor Kinase Type 4 Expression in Sprague‐Dawley Rats

“…It is known that c‐Myc is a transcription factor for GRK4, and there is evidence that ROS increases c‐Myc expression . We, therefore, tried to determine whether PM 2.5 increased GRK4 via the c‐Myc pathway.…”

“…c‐Myc was shown to bind to the promoter region of GRK4 in Burkitt lymphoma cells. Gildea et al found c‐Myc may be involved in the increase in blood pressure in hypertension that is mediated by increased activity of the renin‐angiotensin system and decreased activity of the renal dopaminergic system . Many other studies also report that ROS increased c‐Myc expression .…”

“…However, the molecular mechanisms involved are not well understood. c‐Myc, a human homolog of the avian myelocytomatosis viral oncogene v‐Myc, is involved in cancer progression, which has been implicated in hypertrophy and fibrosis of the heart, atherosclerosis, and hypertension . c‐Myc was shown to bind to the promoter region of GRK4 in Burkitt lymphoma cells.…”

“…It is known that c-Myc is a transcription factor for GRK4, and there is evidence that ROS increases c-Myc expression. [45][46][47] We, therefore, tried to determine whether PM 2.5 increased GRK4 via the c-Myc pathway. Results showed that c-Myc expression was higher in PM 2.5 -treated than control cells ( Figure 4D and 4E), indicating that PM 2.5 might increase GRK4 expression via an increased c-Myc expression.…”

α1‐Adrenoceptor activation of PKC‐ε causes heterologous desensitization of thromboxane receptors in the aorta of spontaneously hypertensive rats

“…It seemed logical to also compare the mRNA expression of different GRK isoforms in aortic smooth muscle of normotensive and hypertensive animals, as PKC may play a role as a GRK regulator (Pronin and Benovic, 1997;Kohout and Lefkowitz, 2003;Lorenz et al, 2003;Gildea et al, 2013). Of the seven known isoforms of GRK reported (Gurevich et al, 2012), the mRNA expressions of GRK1 and GRK7 could not be detected in either WKY or SHR aortic smooth muscle (data not shown).…”